Attwood Stainless Steel Straight Barbed Thru-Hull Fittings Polish your image with these beautiful, durable stainless steel fittings. Why specify plastic parts when these fittings will last the life of the boat. Caution Stainless thru - hull connectors are designed for installation above the water line only. Manufacturer Part Number Hose Size ID Flange Diameter Thread Size Max Hull Thickness Installation Hole Size Barb Length Total Length 66547-3 34 1-78 34 NPSM 1-58 1-58 1-14 3-34 66548-3 1 2-14